THE HAGUE, Netherlands (AP) — An international team of investigators piecing together a criminal case in the July 2014 shooting down of Malaysia Airlines Flight 17 over eastern Ukraine says evidence suggests links between Russia and separatists in the region were closer than previously believed.

The Joint Investigation Team issued a fresh appeal for witnesses Thursday and revealed details of secure communications between Russian officials and rebels in the Donetsk People’s Republic (DPR) rebel group in eastern Ukraine.

In June, the investigators announced that they had charged four people, including three Russians, with murder over their alleged roles in the July 17, 2014, downing of Flight MH17. All 298 passengers and crew on board the Amsterdam-Kuala Lumpur flight were killed.

Investigators say their probe has revealed that “Russian influence on the DPR went beyond military support.”